1. FIELD OF THE INVENTION
The present invention relates to a control system for power supplies in electronic devices and, more particularly, to a digital control system for such power supplies.
2. RELATED ART
Many electronic devices include power supplies that provide an operating voltage to components contained within. Because operating voltages outside of specified limits cause aberrational behavior in solid state components, the power supplies typically regulate the voltage levels with precision.
It is a goal of power distribution systems to provide redundancy in the event of a power supply failure, and a precise division of current-share among power supplies to extend the useful life of each. Many electronic devices, such as PC server systems, require a constant uninterruptible supply of power. These devices are sometimes referred to as "fault-tolerant" or "parallel-redundant" systems. Accordingly, such conventional power supply systems in such devices include two or more power supplies to provide redundancy, a docking backplane to mate with such supplies, and point-of-use planes where the power is dissipated. Typically, each power supply generates power at one or more voltage levels using AC/DC/DC converters. Although the power supplies are identical, one becomes a master power supply and the others become slave power supplies when operated in a current-share mode. Circuitry within the power supply regulates the voltage being output by the power supply over an analog "sense" line.
Disadvantages of the master-slave scheme include:
1. The master supply bears a disproportionate load relative to the slave supply. During power up, the inequitable division of labor is particularly acute: The master supply carries the entire system load initially on power up, after which the slave powers up and shares the load. However, the slave does not bear a full share of the load. The master-slave arrangement shortens the useful life of the master power supply. The charging of the system capacitance creates critical stress on the master supply.
2. The master supply must be able to carry the full load of the electronic device at power up. The slave supply carries no load at power up. As the power requirements of electronic devices have increased, this increases requirements of the master supply. The master-slave scenario increases the cost of the power supplies.
3. The power supplies must be designed to account for periods when the electronic device draws very little power. Without such a design, a low power draw by the device can cause the master and slave supplies to shut themselves off. Thus, power supplies must include a design that works around this special case where the device draws very little load. The design around increases the complexity of the power supplies, increases their costs and adds reliability issues to the supplies.
4. Prior art power supplies are serially redundant which increases the minimum number of required components. "Serial redundancy" occurs from a cascaded series of control circuits: A first control circuit drives a second control circuit that, in turn, drives another control circuit. Typically, each control circuit may have approximately fifteen components. Serial redundancy drives up manufacturing costs and causes reliability issues.
5. Prior art power supplies use bulk capacitors repeatedly within the system prior to the point-of-use plane. The repeated presence of the capacitors cause undesirable effects upon output transient response, overall loop bandwidth, component cost, and reliability.
There is a need in the art for a power conversion and distribution scheme for electronic systems that: minimizes manufacturing complexity, cost, and component count, reduces operating stresses, enables re-use of former power supply designs, eliminates minimum load requirements, encourages simplicity instead of serially-redundancy, and allows marked gains in overall system performance. Further, there is a need in the art for a power distribution system that provides ease in fulfilling the system specifications as required by the electronic device in its realm of use.